Conventionally, in the field of semiconductor device manufacturing technology, generally, a high-quality metallic film, insulating film, or semiconductor film is formed on a surface of a substrate to be processed by MOCVD method.
On the other hand, in recent years, regarding formation of a gate insulating film of a ultrafine semiconductor device in particular, atomic layer deposition (ALD) technology has been studied, in which a high dielectric constant film (referred to as a high-K dielectric film) is formed on a surface of the substrate to be processed by laminating atomic layers one by one.
In the ALD method, metallic compound molecules containing a metallic element constituting the high-K dielectric film are supplied as a material gas in a gas phase to a process space including the substrate to be processed. The metallic compound molecules are chemisorbed on the surface of the substrate to be processed as much as about one molecular layer. Further, after the material gas in a gas phase is purged from the process space, oxidizer such as H2O is supplied, so that the metallic compound molecules adsorbed on the surface of the substrate to be processed are decomposed and a metal oxide film of about one molecular layer is formed.
Further, after the oxidizer is purged from the process space, the above-mentioned step is repeated, so that a metal oxide film of a desired thickness, namely, a high-K dielectric film is formed.
The ALD method uses chemisorption of compound molecules of materials on the surface of the substrate to be processed in this manner and has properties particularly superior in step coverage. The ALD method is capable of forming a high-quality film at a temperature ranging from 200 to 300° C. or less. In accordance with this, the ALD method is considered to be an effective technique not only for forming the gate insulating film of an ultrafast transistor but also for manufacturing a memory cell capacitor of a DRAM where a dielectric film is required to be formed on a ground having a complicated shape.
FIG. 1A and FIG. 1B are diagrams showing an example of a substrate processing apparatus performing the above-mentioned ALD method and an outline of a procedure of the ALD method.
With reference to FIG. 1A and FIG. 1B, a process container 1 holding a substrate 2 to be processed has a first process gas supplying opening 3A disposed on a first side for the substrate 2 to be processed. Also, a first exhaust opening 4A is disposed on a second side for the substrate 2 to be processed, namely, on the opposite side of the first side. Further, the process container 1 has a second process gas supplying opening 3B disposed on the second side and a second exhaust opening 4B disposed on the first side. A first process gas A is supplied to the first process gas supplying opening 3A via a first material switching valve 5A. A second process gas B is supplied to the second process gas supplying opening 3B via a second material switching valve 5B. Moreover, the first exhaust opening 4A is exhausted via a first exhaust volume adjusting valve 6A and the second exhaust opening 4B is exhausted via a second exhaust volume adjusting valve 6B.
First, in a step shown in FIG. 1A, the first process gas A is supplied to the first process gas supplying opening 3A via the first material switching valve 5A and the first process gas A is adsorbed on the surface of the substrate to be processed in the process container 1. In this case, when the first exhaust opening 4A opposite to the first process gas supplying opening 3A is driven, the first process gas A is flown along the surface of the substrate to be processed in a first direction from the first process gas supplying opening 3A to the first exhaust opening 4A.
Next, in a step shown in FIG. 1B, the second process gas B is supplied to the second process gas supplying opening 3B via the second material switching valve 5B and the second process gas B is flown along the surface of the substrate 2 to be processed in the process container 1. As a result of this, the second process gas B affects molecules of the first process gas A previously adsorbed on the surface of the substrate to be processed and a high-dielectric constant molecular layer is formed on the surface of the substrate to be processed. In this case, when the second exhaust opening 4B opposite to the second process gas supplying opening 3B is driven, the second process gas B is flown along the surface of the substrate to be processed in a second direction from the second process gas supplying opening 3B to the second exhaust opening 4B.
By further repeating the steps shown in FIG. 1A and FIG. 1B, a desired high-dielectric constant film is formed on the substrate 2 to be processed.
Preferably, a purge gas is supplied to the process container 1 as appropriate after the step of FIG. 1A or the step of FIG. 1B so as to discharge the first process gas or the second process gas from the process container 1. In accordance with this, it is possible to reduce process time.
Patent Document 1: Japanese Laid-Open Patent Application No. 2002-151489
In the above-mentioned ALD method, a period of time when the first process gas is being supplied and a period of time when the second process gas is being supplied are short. In other words, the step shown in FIG. 1A and the step shown in FIG. 1B continue for about several seconds, for example. Accordingly, it is necessary to promptly change the status of gas supply to the process container 1.
For example, when a flow rate of the first process gas is controlled, generally, a mass flow controller (also referred to as MFC) omitted in FIG. 1A and FIG. 1B is used. However, when the flow rate of the first process gas is controlled, for example, or when a liquid material is used after vaporization in particular, it is difficult in some cases to perform prompt flow rate control in accordance with the above-mentioned steps based on several seconds.
For example, when a material in a liquid state under normal pressure and temperature is used as the first process gas after vaporization, it is necessary to control the flow rate of the material in a liquid state and to use a liquid mass flow controller. For example, materials which may be used in the above-mentioned ALD method include organometallic compound materials and many of these organometallic compound materials are in a liquid state under normal pressure and temperature.
FIG. 2 is a diagram schematically showing a principle of the liquid mass flow controller controlling the flow rate of the liquid material. FIG. 2 schematically shows a portion of an inside of an example of the liquid mass flow controller in an enlarged manner.
With reference to FIG. 2, a liquid mass flow controller 7 shown in the drawing internally includes a flow path 8A of the liquid material and the flow path 8A is branched into a flow path 8B. In the flow path 8B, flow rate detection means 8C is disposed.
Data on the flow rate detected by the flow rate detection means 8C is sent to control means omitted in the drawings and the control means controls flow rate adjusting means 9 in accordance with the flow rate data so as to control the flow rate of the liquid material, the flow rate adjusting means 9 being described in the following.
The flow rate adjusting means 9 includes pressing means 9B, driving means 9A driving the pressing means 9B upward and downward, a diaphragm 9C, and a sheet portion 9D on which the diaphragm 9C is pressed by the pressing means 9B.
When the flow rate of the liquid material is adjusted, the driving means 9A is controlled by the control means, so that vertical movement of the pressing means 9B is controlled and an extent of the diaphragm 9C to be pressed on the sheet portion 9D is adjusted. In accordance with this, conductance between the sheet portion 9D and the diaphragm 9C is adjusted, so that the flow rate of the liquid material is controlled.
However, when the flow rate of liquid is controlled using the liquid mass flow controller, it is difficult to have differential pressure in the front and rear of the flow rate adjusting means 9, so that a variable range of the conductance is required to be larger in comparison with a case where the flow rate of gas is controlled. Accordingly, the driving means 9A is required to have a large driving force (driving range).
As mentioned above, the driving means 9A has the large driving force (driving range), so that when the flow rate is controlled using the liquid mass flow controller, if a setting value is close to 0 or 0, a possibility that the diaphragm 9C may be pressed on the sheet portion 9D is increased in accordance with fluctuation of a control circuit or variation of environmental change such as temperature.
In this manner, once the diaphragm 9C is pressed on the sheet portion 9D, the diaphragm 9C is attached to the sheet portion 9D, so that even when control is performed so as to increase the flow rate again, a period of time for moving the diaphragm 9C to a position corresponding to the predetermined flow rate is increased.
A delay of response time resulting from such characteristics of the liquid mass flow controller has been problematic when the liquid material is vaporized as the process gas and the substrate is processed by the ALD method, for example, in which prompt supply of materials and stop are repeated a number of times.
For example, in order to prevent such a problem, a supply direction switching valve is disposed immediately before the process container 1 shown in FIGS. 1A and 1B, for example. The process gas is flown to an exhaust line bypassing the process container 1 through a switching operation of the switching valve without changing the flow rate set in the liquid mass flow controller. Or the process gas is supplied to the process container 1 by switching supply directions again.
However, in this case, the process gas exhausted from the exhaust line is wasted and consumption of material is increased, so that an increase of cost is problematic. For example, the above-mentioned liquid material containing a metallic element is an expensive material in many cases, so that the waste of the material results in a great loss in terms of cost of substrate processing.